There is a significantly higher incidence of cancer of the colon in men than in women in certain populations. To study the effects of age and sex and sex hormones on colon carcinogenesis, cancer of the colon is being produced in eight groups of male and female BDF1 mice beginning at 6 weeks and 10 months of age by subcutaneous injection of 20 mgm/kg of 1,2-dimethylhydrazine 2-HC1 once a week for twenty weeks. For each sex one group will be intact controls, a second will be castrates, a third group of castrates of each sex will receive carcinogens plus suitable doses of Depo-Estradiol Cypionate, and the fourth group of each castrated sex will be given carcinogens with subcutaneous doses of Depo-Testosterone Cypionate. The dosages of sex hormones will be administered throughout the lifetime of the castrated animals. A fifth group of control animals will be employed to determine the spontaneous tumor incidence in BDF1 mice. The incidence of colon tumors, time of recognition of tumors, and number of colon tumors per animal will be compared with each of the experimental groups. As a second part of the research, cancer of the colon is being induced in C57 Black/6 mice by a combination of 1,2-dimethylhydrazine 2-HCl and methylazoxymethanol and by MNNG intrarectally. Lines of transplantable tumors will be established which vary in their histologic characterics and rate of growth. The transplantable colon tumors will be made available for others needing such materials.